/Engine/Source/Runtime/GeometryCore/Public/Operations/LocalPlanarSimplify.h
The below helper functions are used by SimplifyAlongEdges, but also the similar customized versions of the same algorithm inFMeshBooleanandFMeshSelfUnionas well Test if the triangles connected to a vertex are all coplanar
Whether all the triangles were coplanar
static bool IsFlat ( const [FDynamicMesh3](API\Runtime\GeometryCore\DynamicMesh\FDynamicMesh3) & Mesh, int VID, double DotTolerance, FVector3d & OutFirstNormal )